Photosynthesis, the conversion of light energy to useful chemical energy, is a membrane process. The light-harvesting events of photosynthesis are known to take place in the thylakoid membrane. While the function of chlorophylls in the photosynthetic process is reasonably well defined, the structural organization of the light-harvesting chlorophylls in the thylakoid membrane is a subject of considerable current interest. Possible interactions between chlorophyll and galactolipids in the thylakoid membrane are of particular interest since galactolipids are the major lipid of this membrane. This study proposes the use of deuterium nuclear magnetic resonance (H-2 NMR) as the main spectroscopic technique to study the structure of the galactolipids, and to investigate specific interactions between chlorophyll a and the galactolipids. Selectively deuterated galactolipids will be synthesized by catalytic reduction of the unsaturated galactolipids isolated from the thylakoid membrane. Most H-2 NMR work has so far focused on phospholipid-containing membranes, and essentially no research has been reported on galactolipids, some of which are of considerable clinical relevance. In addition to NMR, other techniques, such as differential scanning calorimetry, are utilized to provide useful complementary information. The proposed research extends previous work on the organization of chlorophyll a in bilayer membranes. This study should yield useful information on the structure, interaction, phase behavior and dynamics of the galactolipids and chlorophyll a in model membrane systems.